Rectifier

ABSTRACT

A rectifier which consists of two coaxial cylindrical electrodes separated by a working gap filled with a low pressure gas and which is controlled by a magnetic field having an axial component; said rectifier being provided with at least one control winding disposed on the external surface, with respect to the working gap, of any of the electrodes and fed with a pulse current, the duration of the current pulses being such that the control magnetic field is removed by the instant the working current pulse switched by the rectifier terminates.

United States Patent [191 Pakin RECTIFIER [76] Inventor: VadilnNik'olaevich Pakin, Zhemchuzhnaya ulitsa 24, kv. 35, Novosibirsk,U.S.S.R.

[22] Filed: Aug. 13, 1971 21 Appl. No.: 171,588

[52] US. Cl. ..3l5/348, 313/157, 313/161 [51] Int. Cl ..H0lj 17/14 [58]Field ofSearch ..313/157, 161;

[56] References Cited UNITED STATES PATENTS l/l97l 10/1968 9/1971Hofmann et a1 ..313/16l Wasa et al. ...3l5/344 X Hofmann ..3l3/l57 X May22,1973

Primary Examiner-Roy Lake Assistant Examiner-James B. MullinsAttorney-Eric H. Waters et a1.

[57] ABSTRACT A rectifier which consists of two coaxial cylindricalelectrodes separated by a working gap filled with a low pressure gas andwhich is controlled by a magnetic field having an axial component; saidrectifier being provided with at least one control winding disposed onthe external surface, with respect to the working gap, of any of theelectrodes and fed with a pulse current, the duration of the currentpulses being such that the control magnetic field is removed by theinstant the working current pulse switched by the rectifier terminates.

2 Claims, 3 Drawing Figures Patented May 22, 1973 3,735,197

2 Sheets-Sheet 1 ZJZA 0 r1 Z (3 Z 2 FIE. J

Patented May 22, 1973 2 Sheets-Sheet 2 N GE RECTIFIER This inventionrelates to gas-discharge devices and, more particularly, to rectifiersdesigned for use in acceleration and plasma techniques and in electricengineering.

Known in the art is a rectifier consisting of two coaxial cylindricalelectrodes separated by a working gap which is filled with alow-pressure gas and which is controlled by a permanent magnetic fieldhaving an axial component.

The rectifying properties of this device are due to the fact that apermanent magnetic field having an axial component is produced near oneof the electrodes, the cathode, by a ferrite block; this magnetic fieldquickly collapses towards the other electrode, the anode, at which it ispractically equal to zero. The gap between the anode and the cathode andthe gas pressure are selected so that the length of the mean electronpath in the gas in the absence of a control magnetic field should beclose to the size of the gap, owing to which the rectifier is capable ofwithstanding high voltages of any polarity. The presence of an axialcomponent in the control magnetic field results in the fact that at theforward polarity of the electrodes the electron path in the gas near thecathode sharply increases, each electron produces several ionizingevents, and an avalanche builds up through which the rectified currentpasses. At the reverse polarity ofthe electrodes, the electrons leavingthe anode are quickly accelerated and, when reaching the region of themagnetic field, bend and increase their path in the gas very little, sothat the rectifier withstands a high reverse voltage.

A disadvantage of this rectifier is that it is a diode uncontrollable intime. Another disadvantage is that a ferrite block of a definite shapeproducing a magnetic field of a definite intensity is rather difficultto manufacture, while the presence of a permanent magnetic field in theanode-to-cathode gap increases the deionization time of the rectifierafter the passage of the working current pulse, which imposesconsiderable limitations on the rate of rise of the reverse voltage atthe rectifier. This rectifier is further disadvantageous in that theworking current is applied from one end of the electrodes, which fact,when the working current pulse has a large duration and high intensity,may cause the plasma to be ejected from the working zone by the magneticpressure of the working current to the free end so that a pinch effectand quick destruction of the electrodes may result.

An object of the present invention is to obviate the above mentioneddisadvantages by providing a rectifier which is controlled by apulse-type magnetic field, has a small deionization time, is simple inconstruction, easy to manufacture and reliable in operation.

With this object in view, the rectifier according to the invention isprovided with at least one control winding disposed on the externalsurface, with respect to the working gap of any of the electrodes andfed with pulse current, the duration of the current pulses being suchthat the control magnetic field is removed the instant the workingcurrent pulse switched by the rectifier terminates.

The control winding should be preferably made bifilar, the winding pitchbeing larger than the working gap between the electrodes.

It is also preferable that the control winding should be made sectional.

To enable the control magnetic field to penetrate into the working gapand effectively to remove the control field the instant the workingcurrent pulse terminates, the electrodes should be preferably made froma material having a sufficiently high resistivity and low permeabilityfor the given thickness of the electrode walls and the duration of thecontrol magnetic field pulse.

To prevent the plasma from being ejected to the ends of the electrodesand increase the operational reliability of the rectifier, the workingcurrent should be preferably applied symmetrically to both ends of theelectrodes.

For symmetrical application of the current to the electrode ends, diskflanges should be preferably attached at the electrode ends to which theworking current should be symmetrically fed along the circumference.

For reliable protection of the insulators against the plasma ejectedfrom the discharge gap and for reduction of the size of the insulators,the current should be preferably applied with the help of coaxialcylinders of a diameter much smaller than the diameter of the workingelectrodes, said cylinders being attached at the electrode ends.

The invention will be better understood from the following descriptionof its specific embodiment when read in connection with the accompanyingdrawings, in which:

FIG. 1 is a sectional view of a rectifier with disk flanges at theelectrode ends, according to the invention;

FIG. 2 is a sectional view of a rectifier with coaxial cylindricalleads, according to the invention;

FIG. 3 is a time graph illustrating the operation of the rectifier,according to the invention.

The rectifier shown in FIG. 1 comprises an outer electrode 1 and aninner electrode 2 designed as coaxial stainless steel cylindersseparated by a gap 3 and terminating in shaped disk flanges 4 and 5which are isolated from each other by shaped ring insulators 6 and usedso as to symmetrically apply the working current to the electrodes 1 and2 of the rectifier simultaneously from both ends.

A helical groove provided on the outer electrode 1 accommodates abifilar control winding 7 made from an insulated copper strap. The pitchof the control winding 7 is made several times (e.g. four times) largerthan the size of the gap 3. The control winding 7 is sectionalized. Therectifier is also provided with pipe connections 8 and holes 9 forfeeding the gas to, and evacuating it from, the working gap 3.

Apart from these components the rectifier shown in FIG. 2 comprisescoaxial cylinders 10 and 11 which are attached on the disk flanges 4 and5 and which have diameters much smaller than those of the electrodes 1and 2.

The time graph in FIG. 3 shows a curve 12 and a the control currentpulse terminates and the instant t =t to the moment at which the workingcurrent pulse terminates or, in other words, drops to zero.

The rectifier operates as follows.

At the instant i= a control current pulse is applied to the controlwinding 7. The magnetic field produced by the control current penetratesthrough the wall of the electrode 1 and at the instant I, which isdetermined by the voltage at which the rectifier reaches a criticalvalue a breakdown occurs in the rectifier due to a sharp increase in theelectron path in the gas. I

At current densities up to about 3A/cm the rectifier operates with aglow discharge completely controlled by the magnetic field, the voltagedrop across the discharge being equal to or greater than 350 V. As thecurrent density increases the glow discharge passes to an arc dischargewith a voltage drop of about 100-50 V. Since the arc discharge is notcontrolled by an external magnetic field, this field may be removedafter the arc is struck and the discharge is extinguished the first timethe working current passes through zero. As at the instant t themagnetic field is removed, the electron path in the gas is small andclose to the size of the working gap 3 and the rectifier safelywithstands a high voltage of any polarity. If, however, by the instant 1corresponding to the zero working current the magnetic field is notremoved, the electron path remains large, the deionization and ionrecombination time is great and the rectifier passes current in thereverse direction, forward direction and so on, until the controlmagnetic field is removed and the arc is naturally extinguished thefirst time the working current passes through zero after the removal ofthe control field.

The advantage of the present invention is that the rectifier iscontrolled in time, practically irrespective of the electrode polarityand, therefore, can be used for switching single pulses of any polarityor successive trains of pulses of any polarity. Another advantage of therectifier described herein is that its magnetic control means is easy tomanufacture as being in the form of a conventional winding made fromconductors. The shape and connection of the winding are immaterial,though a bifilar winding with a pitch several times larger than the sizeof the working gap is preferable.

The rectifier has a small deionization and ion recombination time as thecontrol field is absent at the instant the working current pulseterminates.

Owing to the fact that current is symmetrically applied from both endsof itselectrodes the rectifier has a reliable balanced construction withleads having small spurious inductance and low resistance.

The use of a sectional winding enables the rectifier to operate with anarc discharge in the gas even at low working currents without currentinterruption.

What is claimed is:

1. A rectifier comprising an insulator; a first cylindrical electrode; asecond cylindrical electrode disposed coaxially with respect to saidfirst electrode and separated therefrom by said insulator; there beingprovided a working gap between said electrodes, a low-pressure gasfilling said gap; said electrodes having external surfaces and oppositeends; a control winding to produce a pulsed control magnetic fieldhaving an axial component with said working gap, said control windingbeing disposed on the external surface, with respect to said workinggap, of at least one of said electrodes; and means for the axial,symmetrical supply of current to be switched simultaneously to both endsof both electrodes, said means being in the form of disk flanges securedon both ends of said electrodes.

2. A rectifier as claimed in claim 1 comprising coaxial cylinders andwherein said disk flanges are coupled with the co-axial cylinders whichhave a substantially small diameter than said electrodes.

1. A rectifier comprising an insulator; a first cylindrical electrode; asecond cylindrical electrode disposed coaxially with respect to saidfirst electrode and separated therefrom by said insulator; there beingprovided a working gap between said electrodes, a low-pressure gasfilling said gap; said electrodes having external surfaces and oppositeends; a control winding to produce a pulsed control magnetic fieldhaving an axial component with said working gap, said control windingbeing disposed on the external surface, with respect to said workinggap, of at least one of said electrodes; and means for the axial,symmetrical supply of current to be switched simultaneously to both endsof both electrodes, said means being in the form of disk flanges securedon both ends of said electrodes.
 2. A rectifier as claimed in claim 1comprising coaxial cylinders and wherein said disk flanges are coupledwith the co-axial cylinders which have a substantially small diameterthan said electrodes.